This invention generally relates to ink jet printers and more particularly relates to a method for permanent alteration of a print head for correcting mis-direction of ink drops emitted therefrom.
An ink jet printer produces images on a receiver by emitting or ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace. The printers can be either xe2x80x9ccontinuousxe2x80x9d drop or drop xe2x80x9con demandxe2x80x9d.
xe2x80x9cContinuousxe2x80x9d ink jet printers utilize electrostatic charging tunnels that are placed close to the point where ink droplets are being ejected in the form of a stream. Selected ones of the droplets are electrically charged by the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the recording medium. Also know the art of continuous ink jet printers includes, inter alia, xe2x80x9cthermally steeredxe2x80x9d ink jets, in which the asymmetric application of heat in portions of a nozzle ring causes the deflection of droplets in a stream, as described in commonly assigned U.S. Pat. No. 6,078,821, Oct. 17, 1997, entitled xe2x80x9cContinuous Ink Jet Printer With Asymmetric Heating Drop Deflectionxe2x80x9d, by Chwalek et al.
In the case of xe2x80x9con demandxe2x80x9d ink jet printers, at every ink emitting or ejecting orifice or nozzle a pressurization actuator is used to produce the ink jet droplet. In this regard, either one of two types of actuators may be used. These two types of actuators are heat actuators (as commercialized, for example, by Canon Inc. under the trade name xe2x80x9cBubble Jetxe2x80x9d and by the Hewlett Packard Company) and piezoelectric actuators (as commercialized, for example, by Epson). With respect to heat actuators, a heater placed at a convenient location heats the ink and a quantity of the ink will phase change into a gaseous steam bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled to the recording medium. With respect to piezoelectric actuators, a piezoelectric material is used, which piezoelectric material possesses piezoelectric properties such that an applied electric field will produce a mechanical stress in the material. The most commonly produced piezoelectric ceramic is lead zirconate titanate. Also known in the art of drop on demand printing are devices in which heat is applied symmetrically to the air-ink meniscus by means of a nozzle rim disposed around the ink ejection orifice to effect droplet ejection as taught in EP00890437A3 by Silverbrook. The nozzle rim is generally made of a resistive heater material such as doped polysilicon which is heated by the passage of an electrical current.
In the instance of both continuous and on demand ink jet printers, it has been found that when larger numbers of ink ejecting orifices or nozzles are formed on a print head, small variations in the directional path of ink drop emission or ejection from nozzle to nozzle or orifice to orifice will be present. Such variations typically result from manufacturing non-uniformities; and cause reduced image quality and in the instance of continuous ink jet systems, catastrophic failure if the variation in drop direction is sufficient to prevent guttering. Such variant nozzles, due to the precise requirements for ink droplet size, and the small size of the orifices and nozzles cannot be repaired, absent burdensome and disadvantageous cost. Therefore, corrections tend to be temporary adjustments. In the case of continuous ink jet printers utilizing electrostatic deflection, some correction for misdirection of drops has been achieved by adjusting the voltages applied to each deflection electrode individually during the printing of each drop. However this method is expensive and generally capable of adjusting the direction of drop deflection in only a single direction. In the case of thermally steered ink jet printers, some correction for misdirection of drops can be achieved by adjusting the voltages applied to heater segments during the printing of each drop. However this method is also expensive and difficult to manufacture. Both corrective methods are unduly complex because the correction must be re-applied for each printed drop.
Therefore, there is a need for a manner of precisely altering a print head to redirect errant ink droplets without having to replace the ink emitting nozzles and orifices.
An object of the present invention is to provide a method and an article for altering a print head in order to redirect the errant path of emitted or ejected ink drops, in a permanent fashion which does not require replacing the ink ejecting orifices (also sometimes referred to as xe2x80x9cnozzlesxe2x80x9d).
With this object in view, a primary aspect of the present invention resides in an ink jet print head having a surface, defining at least one orifice therethrough for xe2x80x9cemittingxe2x80x9d (also sometimes referred to as xe2x80x9cejectingxe2x80x9d) ink droplets from an ink source onto a xe2x80x9cprintingxe2x80x9d (sometimes referred to as xe2x80x9crecordingxe2x80x9d) medium, and at least one element disposed around the orifice. That element is selectably removable for altering a directional path of the emitted ink droplets. The emitted ink droplets are thereby redirected from the at least one orifice by asymmetrically removing a portion of the element disposed around the orifice.
According to an exemplary aspect of the present invention, during fabrication or manufacture of the printhead, a deformation control element made from nitride, polysilicon, metal, etc., is applied under mechanical, stress from the energy of its application. For example, plasma or vapor deposition techniques can be employed to deposit the elements symmetrically around each orifice and atop an orifice membrane region. Because the element is symmetrically deposited around the orifice, the direction of an ink drop emitted therefrom is not changed by the presence of the deposited material so long as the membrane region underneath the deposit is also symmetrical. Upon detection of a variant orifice, a portion of the deformation control element is removed, for example, by laser ablation in order to asymmetrically alter an aspect of the orifice such that droplets follow an altered directional path.
According to another exemplary aspect of the present invention, applied advantageously to thermally steered ink jet printers, during print head fabrication, an element of a thermal conduction control material, for example, an evaporated metal, is deposited symmetrically surrounding each nozzle or orifice over the region of the orifice membrane. Because this material is symmetrically disposed, the direction of an emitted or ejected droplet is not changed if the underlying membrane and nozzle are also symmetrical, regardless of whether the thermal conduction material is energized or heated. Upon detection of a variant nozzle, a portion of the thermal conduction control material is removed, for example, by laser ablation, to the extent that during heater activation, the heat applied is asymmetric in a way so as to cause the heater deflected droplets to be directed or steered along a desired directional path. In the absence of heater activation, no alteration in deflection of the droplets occurs.
According to another exemplary aspect of the present invention, during print head fabrication, an element including a symmetric fluid contact ring is positioned surrounding each nozzle or orifice for controlling direction of ink droplet ejection or emission by the effect of surface tension force, both for deflected and undeflected droplet emission. Upon detection of a variant nozzle, a portion of the fluid contact ring is removed, for example by laser ablation, to the extent that the direction path of the ejected ink droplets is correspondingly altered.
According to still another exemplary aspect of the present invention, during print head fabrication, an element including a symmetrical hydrophobic material for controlling ink meniscus profile is formed surrounding each nozzle or orifice. Because the hydrophobic material is symmetrically disposed, the direction of an emitted or ejected ink droplet is not changed. Upon detection of a variant nozzle or orifice, a circumferential portion of the hydrophobic material is removed, again for example by laser ablation, to the extent that the directional path of emitted or ejected ink droplets is correspondingly altered.
According to still another exemplary aspect of the present invention, during print head fabrication, a symmetrical lateral flow blocking element for controlling ink meniscus profile is formed surrounding each nozzle or orifice. Because the lateral flow blocking element is symmetrically disposed, the direction of an emitted or ejected ink droplet is not changed. Upon detection of a variant nozzle, a circumferential portion of the lateral flow blocking element is removed, again for example by laser ablation, to the extent that the directional path of emitted or ejected ink droplets is correspondingly altered.
According to still another exemplary aspect of the present invention, applied advantageously to thermally steered ink jet printers, during print head fabrication, an element including a symmetrical heat blocking or insulating layer for controlling ink meniscus profile is formed surrounding each nozzle or orifice. Because the heat blocking or insulating layer is symmetrically disposed, the direction of an emitted or ejected ink droplet is not changed. Upon detection of a variant nozzle, a circumferential portion of the heat blocking or insulated layer is removed, again, for example by laser ablation, to the extent that the directional path of emitted or ejected ink droplets is correspondingly altered.
A feature of the present invention is a symmetrical element extending around an ink ejecting orifice or nozzle, the element being selectably removable or alterable for correspondingly altering a directional characteristic of the emitted or ejected ink droplets.
Another feature of the present invention is the capability to alter an ink jet print head to correct directional deficiencies, the alteration being permanent in the sense that the corrective procedure need not be reapplied to each printed drop.
Another feature of the present invention is the capability to alter an ink jet print head to correct directional deficiencies in ink emission or ejection without effecting changes to the orifice or nozzle itself.
An advantage of the present invention is that image quality is improved and catastrophic failures due to guttering problems are avoided in the case of continuous ink jet printers.
Another advantage of the present invention is that the alteration of the print head provides a cost advantage over alternative corrective steps.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there are shown and described illustrative embodiments of the invention.